Andrew C. Klein

A model for waterside oxidation of zircaloy fuel cladding in pressurized water reactors

Abstract A model is developed to simulate the oxidation of Zircaloy fuel rod cladding exposed to pressurized water reactor operating conditions. The model is used to predict the oxidation rate for both ex- and in-reactor conditions in terms of the weight gain and oxide thickness. Comparisons of the model predictions with experimental data show very good agreement.

Experimental simulations and heat transfer parameter measurements of film condensation on a rotating flat plate

Abstract A rotating flat-plate condensation experiment has been developed to investigate the heat transfer characteristics of a rotating flat-plate radiator. The condensing surface is cooled to simulate the rejection of heat to a cold surface. The working fluid is superheated steam. The results obtained include relationships between the overall heat transfer coefficient and the temperature difference between the working fluid and a cold environment, both placed in dimensionless groups, and plate angular rotational speeds. This empirical relationship is useful for choosing the optimum rotational speed for a rotating flat-plate radiator given a desired heat rejection load. This study also provides the basis for designing new heat rejection systems using centrifugal forces and condensation phenomena in both space and ground applications.

Anomalous heat output from Pd cathodes without detectable nuclear products

A series of experiments has been conducted to explore the effects of electrolyzing heavy water (D2O) using palladium and platinum electrodes. Over 40 weeks of experimental runs have been conducted in four cells which electrolyze heavy water using palladium and platinum electrodes. Tritium production, neutron and gamma radiation, and cell temperatures were monitored simultaneously and continuously throughout the runs. These experiments have resulted in seven elevated temperature events similar to those claimed by Pons and Fleischmann, with no correlating detection of nuclear products. The seven events which have occurred to date all take the same general form in which the apparent heat output of a cell, as seen in terms of the change in cell fluid temperature, increases in a distinct and significant step. A single light water cells, identical in all respects to those using heavy water, has been operated for over 15 weeks and has produced no temperature excursions, and also no nuclear products.

Modeling the energy transport through a thermionic fuel element

A thermionic fuel element is complex both in terms of its construction and in its operating principles. An energy transport analysis of such a device must consider the heat transfer properties of the different materials as well as the modes of heat transfer from the various interfaces. A computer code (TFEHX) to model the thermal and electrical performance of a TFE has been developed. This code uses finite element methods to compute the temperature profile within the TFE components, as well as the electrical output from the TFE. The thermionic emission properties are computed using a phenomenological model for the cesium diode converter. The code allows the specification of various TFE design parameters, including the spatial dependence of the thermal power and the TFE geometric and material properties.

Advanced thermionic reactor systems design code

An overall systems design code is under development to model an advanced in‐core thermionic nuclear reactor system for space applications at power levels of 10 to 50 kWe. The design code is written in an object‐oriented programming environment that allows the use of a series of design modules, each of which is responsible for the determination of specific system parameters. The code modules include a neutronics and core criticality module, a core thermal hydraulics module, a thermionic fuel element performance module, a radiation shielding module, a module for waste heat transfer and rejection, and modules for power conditioning and control. The neutronics and core criticality module determines critical core size, core lifetime, and shutdown margins using the criticality calculation capability of the Monte Carlo Neutron and Photon Transport Code System (MCNP). The remaining modules utilize results of the MCNP analysis along with FORTRAN programming to predict the overall system performance.

System modeling for the advanced thermionic initiative single cell thermionic space nuclear reactor

Incore thermionic space reactor design concepts which operate in a nominal power output range of 20 to 40 kWe are described. Details of the neutronics, thermionic, shielding, and heat rejection performance are presented. Two different designs, ATI‐Driven and ATI‐Driverless, are considered. Comparison of the core overall performance of these two configurations are described. The comparison of these two cores includes the overall conversion efficiency, reactor mass, shield mass, and heat rejection mass. An overall system design has been developed to model the advanced incore thermionic energy conversion based nuclear reactor systems for space applications in this power range.

Modeling and analysis of a heat transport transient test facility for space nuclear systems

Abstract The purpose of this study was to design a robust test facility for a small space nuclear power system and model its physical behavior under different scenarios. The test facility will be used to simulate a 1- to 10-kW(electric) nuclear reactor, its electrical generation, and heat removal capabilities. This simulator will be used to explore, test, and understand the steady-state and transient operation capabilities of small space nuclear power systems. Currently, the system is planned to operate on a variable, electrical heat source directly connected to heat pipes. The heat pipes are to be stainless steel with a water working fluid. These heat pipes will then be connected to a power conversion simulator or actual power conversion technologies. The power conversion simulator is connected to a radiator using a water-based heat pipe network using fins and connecting plates in a cylindrical geometry. Modeling of the facility was performed using the SolidWorks Flow Simulation package. Flow Simulation was used to analyze startup, heat pipe failures, and loss of power conversion with the end goal of finding safe operational transient scenarios for the transient test facility.

Comparison of Tungsten and Molybdenum Based Emitters for Advanced Thermionic Space Nuclear Reactors

Variations to the Advanced Thermionic Initiative thermionic fuel element are analyzed. Analysis included neutronic modeling with MCNP for criticality determination and thermal power distribution, and thermionic performance modeling with TFEHX. Changes to the original ATI configuration include the addition of W‐HfC wire to the emitter for high temperature creep resistance improvement and substitution of molybdenum for the tungsten base material. Results from MCNP showed that all the tungsten used in the coating and base material must be 100% W‐184 to obtain criticality. The presence of molybdenum in the emitter base affects the neutronic performance of the TFE by increasing the emitter neutron absorption cross section. Due to the reduced thermal conductivity for the molybdenum based emitter, a higher temperature is obtained resulting in a greater electrical power production. The thermal conductivity and resistivity of the composite emitter region were derived for the W‐Mo composite and used in TFEHX.

Materials compatibility issues for fabric composite radiators

Short term materials compatibility tests have been completed on potential materials to be used in fabric composite radiators for space applications. Specific materials tested include copper, aluminum, titanium, FEP Teflon tubing, and three high strength fabric fibers: alumina‐boria‐silica, silicon carbide, and silicon dioxide. These materials have been exposed to pure water, methanol, and acetone for periods of time up to 5000 hours at variety of appropriate temperatures.

Feasibility Study of a Soluble Boron–Free Small Modular Integral Pressurized Water Reactor

Abstract The elimination of soluble boron in the operation of small modular integral pressurized water reactors creates several advantages. Most of these advantages are realized by the core simplification brought on by removing the corrosive effects of soluble boron. Piping, pumps, and tanks associated with soluble boron can be completely eliminated, bringing a significant economic and safety benefit. Additionally, a whole class of accidents related to boron dilution would be eliminated by design, and any loss-of-coolant event would not be affected by the presence of soluble boron. However, removing soluble boron creates its own set of specific challenges that must be overcome. In traditional pressurized water reactors, soluble boron is used in conjunction with burnable poisons to suppress excess initial reactivity. Since boron is diluted in the coolant, its presence is felt uniformly throughout the core, and thus it uniformly reduces the excess initial reactivity. In any boron-free design, an acceptable alternative to boron must be found through the use of the other two mechanisms for reactivity control: burnable poisons and control rods. However, both methods pose challenges. Control rods are actively controlled but are discrete absorbers, locally impacting the core where they are inserted. Since they are inserted from the top of the core, their presence negatively impacts the axial neutron flux profile. This axial flux imbalance creates undesirable peaking factors, leading to reduced operating margins. Thus, the main challenge in any boron-free design concerns excess reactivity suppression and active reactivity control while maintaining a proper axial flux profile and reduced peaking factors. This paper demonstrates that an advanced control rod algorithm with multiple control rod banks can be used for this purpose to satisfy the criteria for success.